Atomic clocks form the basis of international time keeping, and are widely used in navigation, communications and network management. The realisation of the unit of time plays a central role within the SI because of its unequalled precision and because it is also used in the realisations of other units, such as the metre, volt and ampere. The most advanced optical clocks have now reached a degree of reproducibility that exceeds that of primary caesium atomic clocks by more than an order of magnitude. This JRP addresses the development of ultra-precise optical clocks using laser-cooled trapped ions. The combination of laser cooling and ion trapping provides an ideal spectroscopic system that permits the observation of unperturbed atomic frequencies, thus laying the foundation for atomic clocks of the highest accuracy.

This JRP will improve the performance of trapped ion optical clocks through targeted improvements in the key components of the clocks, i.e. the ion traps and interrogation lasers. It will develop trap architectures for multiple ions in order to improve the signal to noise ratio, leading to improved stability and reduced averaging time. Lasers with improved short-term stability will result in reduced linewidths, improving the stability of the clock and permitting sensitive studies of small systematic frequency shifts. The development of an extended automated experimental control will also provide these instruments with the level of reliability required for their application in time scale steering.

The main contributions to the systematic uncertainty in optical clocks with trapped ions arise from the interaction of the ions with electric and magnetic fields; this includes the field of blackbody radiation emitted by the trap and vacuum system. Control of these fields and precise knowledge of the relevant atomic sensitivity factors will reduce the systematic uncertainty significantly. This JRP will evaluate systematic uncertainties and stabilities across three representative ion species: 27Al+, 88Sr+, and 171Yb+. The aim is to identify the most favourable candidate(s) for optical clocks in terms of performance limitations and technical complexity in various applications.